Process for upgrading light paraffins

ABSTRACT

The present invention relates to a process for producing aromatic compounds from a hydrocarbon gas containing paraffinic hydrocarbons under conversion conditions in the presence of a catalyst comprising a gallosilicate molecular sieve and a platinum metal component.

BACKGROUND OF THE INVENTION

The present invention is directed to a process for upgrading lightparaffins such as ethane, propane, and butanes. Interest in upgradingthese light paraffins has been growing due to recent and anticipatedchanges in refinery processing schemes which resulted and will result ina greater supply of such light paraffins. These changes include: thehigher severity operation of the reforming process in order to maintaina high octane rating in the absence of or reduction of the lead contentin gasoline; the lowering of reid vapor pressure (RVP) specifications;the increased use of oxygenates such as methyl tertiary butyl ether(MTBE) and ethanol resulting in the removal of butanes from the gasolinepool; the increased demand for jet fuel necessitating increased gas oilhydrocracking resulting in more light gas production, and the increasein operating temperatures in fluidized catalytic crackers resulting inmore light gas production. Thus, there is great incentive to investigatemeans for converting these materials into more valuable liquids such astransportation fuels or chemical feedstocks.

The upgrading or conversion of light paraffinic gases and synthesis gashas previously been carried out in the presence of gallium-based orgallium-containing catalysts.

U.S. Pat. No. 4,543,347 (Heyward et al.) discloses a catalystcomposition suitable for converting synthesis gas to hydrocarbons whichis a mixture of zinc oxide and an oxide of at least one metal selectedfrom gallium and iridium, an oxide of at least one additional metalcollected from the elements of Group IB, II through V, VIB and VIIIincluding the lanthanides and actinides and a porous crystallinetectometallic silicate.

U.S. Pat. No. 4,490,569 (Chu et al.) discloses a process for convertingpropane to aromatics over a zinc-gallium zeolite. This zeoliteoptionally may also contain palladium. More specifically, the catalystcomposition used in the instant patent consists essentially of analuminosilicate having gallium and zinc deposited thereon or analuminosilicate in which cations have been exchanged with gallium andzinc ions wherein the aluminosilicate is selected from the group knownas ZSM-5 type zeolites.

U.S. Pat. No. 4,585,641 (Barri et al.) discloses crystallinegallosilicates which may be impregnated, ion exchanged, admixed,supported or bound for catalyzing a reaction such as alkylation,dealkylation, dehydrocyclodimerization, transalkylation, isomerization,dehydrogenation, hydrogenation, cracking, hydrocracking, cyclization,polymerization, conversion of carbon monoxide and hydrogen mixturesthrough hydrocarbons and dehydration reaction. The metal compounds whichmay be used for ion exchange or impregnation may be compounds of any oneof the groups of metals belonging to Groups IB, IIB, IIIA, IVA, VA, VIB,VIIB and VIII according to the Periodic Table. Specifically, preferredcompounds include copper, silver, zinc, aluminum, gallium, indium,vanadium, lead, antimony, bismuth, chromium, molybdenum, tungsten,manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium,platinum, radium, thorium and the rare earth metals. Patentees describetheir gallosilicate as "Gallo Theta-1" in contradistinction to anMFI-type gallosilicate which has a substantially different X-raydiffraction pattern.

U.S. Pat. No. 4,350,835 (Chester et al.) relates to a catalytic processfor converting gaseous feedstocks containing ethane to liquid aromaticsby contacting the feed in the absence of air or oxygen under conversionconditions with a crystalline zeolite catalyst having incorporatedtherein a minor amount of gallium thereby converting the ethane toaromatics. The gallium is present in the catalyst as gallium oxide or asgallium ions if cations in the aluminosilicate have been exchanged withgallium ions. The patent further discloses that the original alkalimetal of the zeolite, when it has been synthesized in the alkali metalform, may be converted to the hydrogen form or be replaced by ionexchange with other suitable metal cations of Groups I through VIII ofthe Periodic Table, including nickel, copper, zinc, palladium, calciumor rare earth metals.

European Patent Application 0 107 876 discloses a process for producingan aromatic hydrocarbon mixture from a feedstock containing more than 50wt. % C₂ through C₄ paraffins. Specifically the process is carried outin the presence of crystalline gallium-silicate having a SiO₂ /Ga₂ O₃molar ratio of 25 to 250 and a Y₂ O₃ /GaO₃ molar ratio lower than 1where Y can be aluminum, iron, cobalt or chromium. The disclosure alsoteaches a two-step silicate treatment comprising a coke deposition and acoke burn-off with an oxygen-containing gas.

European Patent Application 0 107 875 similarly discloses a process forproducing an aromatic hydrocarbon mixture from a feedstock comprisingmore than 50 wt. % of C₂ through C₄ paraffins. This process is carriedout in the presence of a crystalline gallium-silicate, having a SiO₂/Ga₂ O₃ molar ratio of 25 to 100 and a Y₂ O₂ /Ga₂ O₃ molar ratio lowerthan 1 where Y can be aluminum, iron, cobalt or chromium.

Light paraffinic gases have also been upgraded to liquid aromatics inthe presence of crystalline aluminosilicate zeolite catalysts havingincorporated therein a minor amount of a metal selected from GroupsVIII, IIB, and IB of the Periodic Table. For instance, U.S. Pat. No.4,120,910 (Chu) discloses copper-zinc-HZSM-5, platinum-HZSM-5,copper-HZSM-5, and zinc-HZSM-5 catalysts suitable for upgrading agaseous paraffinic hydrocarbon feed to aromatic compounds.

It has now been discovered that C₂ through C₅ light paraffins can mosteffectively be upgraded by the catalytic process of the presentinvention minimizing methane and ethane production while simultaneouslyminimizing the production of undesirable heavy aromatics such asnaphthalenes.

SUMMARY OF THE INVENTION

Briefly stated, in a broad aspect, this invention relates to a processfor producing aromatic compounds from a hydrocarbon gas containingparaffinic hydrocarbons under conversion conditions in the presence of acatalyst comprising a gallosilicate molecular sieve and a platinum metalcomponent.

DETAILED DESCRIPTION OF THE INVENTION

The present invention deals with the conversion to aromatic compounds ofa hydrocarbon gas containing paraffinic hydrocarbons. A particularlysuitable feedstock for use in the present invention contains C₂ throughC₅ light paraffins or any fraction thereof in an amount where the gascontains at least 50 wt. % of such paraffins. A preferred feedstock isone which has a high propane content, typically, a liquefied petroleumgas (LPG). In addition to the mentioned paraffins, the feedstock maycontain other light gases such as methane, ethane, propane, butene,isobutane, butadiene, and paraffins and olefins with five or more carbonatoms per molecule. These feedstocks are generally available fromseveral sources in a refinery as elucidated above.

The process of the invention provides for the direct conversion of thelight paraffinic gases to valuable aromatic hydrocarbons such asbenzene, toluene, and xylenes. These aromatics can be used as anadditive component to increase the octane number of gasoline or as rawmaterials in the petrochemical industry.

The process of the invention selectively provides for a high yield ofbenzene, toluene, and xylenes in the C₄ + product fraction whileminimizing the yield of light C₁ through C₂ gases and C₉ + aromaticcompounds in the product fraction.

Broadly, the catalyst employed according to the process of the presentinvention comprises a gallosilicate molecular sieve component and aplatinum metal component. The gallosilicate can be prepared usingconventional methods known to those skilled in the art. A suitablemethod is disclosed in European Patent Application 01 107 875 which isincorporated herein by reference.

In another method the gallosilicate crystalline molecular sieves of thisinvention are characterized by the representative X-ray pattern listedin Table 1 below and by the composition formula:

    0.9±0.2 M.sub.2/n O:Ga.sub.2 O.sub.3 :ySiO.sub.2 :zH.sub.2 O

wherein M is at least one cation, n is the valence of the cation, y isbetween 4 and about 600, and z is between 0 and about 160. It isbelieved that the small gallium content of the sieves is at least inpart incorporated in the crystalline lattice. Various attempts to removethe gallium from the gallosilicate sieves by exhaustive exchange withsodium, ammonium, and hydrogen ions were unsuccessful and therefore, thegallium content is considered nonexchangeable in the instant sievesprepared according to the present method.

                  TABLE 1                                                         ______________________________________                                                   Assigned               Assigned                                    d-Spacing Å (1)                                                                      Strength (2)                                                                             d-Spacing Å (1)                                                                       Strength (2)                                ______________________________________                                        11.10 ± 0.20                                                                          VS         3.84 ± 0.10                                                                            MS                                          9.96 ± 0.20                                                                           MS         3.71 ± 0.10                                                                            M                                           6.34 ± 0.20                                                                           W          3.64 ± 0.10                                                                            W                                           5.97 ± 0.20                                                                           W          2.98 ± 0.10                                                                            VW                                          5.55 ± 0.20                                                                           W                                                                  4.25 ± 0.10                                                                           VW                                                                 ______________________________________                                         (1) Copper K alpha radiation                                                  (2) VW = very weak; W = weak; M = medium; MS = medium strong; VS = very       strong                                                                   

A gallosilicate molecular sieve useful in this invention can be preparedby crystallizing an aqueous mixture, at a controlled pH, of a base, agallium ion-affording material, an oxide of silicon, and an organictemplate compound.

Typically, the molar ratios of the various reactants can be varied toproduce the crystalline gallosilicates of this invention. Specifically,the molar ratios of the initial reactant concentrations are indicatedbelow:

                  TABLE 2                                                         ______________________________________                                                                      Most                                                        Broad    Preferred                                                                              Preferred                                       ______________________________________                                        SiO.sub.2 /Ga.sub.2 O.sub.3                                                                  4-200      10-150   20-100                                     Organic base/SiO.sub.2                                                                      0.5-5      0.05-1   0.1-0.5                                     H.sub.2 O/SiO.sub.2                                                                          5-80      10-50    20-40                                       Template/SiO.sub.2                                                                          0-1        0.01-0.2 0.02-0.1                                    ______________________________________                                    

By regulation of the quantity of gallium (represented as Ga₂ O₃) in thereaction mixture, it is possible to vary the SiO₂ /Ga₂ O₃ molar ratio inthe final product. In general, it is desirable to have the galliumcontent of the gallosilicate sieve of this invention between about 0.1and about 8 percent by weight of gallium. More preferably, the amount ofgallium should be between about 0.2 and about 6 weight percent galliumand, most preferably, between about 0.3 and about 4 weight percent ofgallium. Too much gallium in the reaction mixture appears to reduce thesieve crystallinity which reduces the catalytic usefulness of the sieve.

More specifically, a material useful in the present invention isprepared by mixing a base, a gallium ion-affording substance, an oxideof silicon, and an organic template compound in water (preferablydistilled or deionized). The order of addition usually is not criticalalthough a typical procedure is to dissolve the organic base and thegallium ion-affording substance in water and then add the templatecompound. Generally, the silicon oxide compound is added with mixing andthe resulting slurry is transferred to a closed crystallization vesselfor a suitable time. After crystallization, the resulting crystallineproduct can be filtered, washed with water, dried, and calcined.

During preparation, acidic conditions should be avoided. Advantageously,the pH of the reaction mixture falls within the range of about 9.0 toabout 13.0; more preferably between about 10.0 and about 12.0 and mostpreferably between about 10.5 and 11.5.

Examples of oxides of silicon useful in this invention include silicicacid, sodium silicate, tetraalkyl silicates, and Ludox, a stabilizedpolymer of silicic acid manufactured by E. I. DuPont de Nemours & Co.Typically, the oxide of gallium source is a water-soluble galliumcompound such as gallium nitrate or gallium acetate or another galliumcompound, the anion of which is easily removed during sieve calcinationprior to use. Water insoluble gallium compounds such as the oxide can beused as well.

Cations useful in the formation of the gallosilicate sieves include thesodium ion and the ammonium ion. The sieves also can be prepareddirectly in the hydrogen form with an organic base such asethylenediamine.

The acidity of the gallosilicate sieves of this invention is high asmeasured by the Hammett H_(o) function which lies in the neighborhood ofabout -3 to about -6.

Organic templates useful in preparing the crystalline gallosilicateinclude alkylammonium cations or precursors thereof such astetraalkylammonium compounds, especially tetra-n-propylammoniumcompounds. A useful organic template is tetra-n-propylammonium bromide.Diamines, such as hexamethylenediamine, can be used.

The crystalline gallosilicate molecular sieve can be prepared bycrystallizing a mixture of sources for an oxide of silicon, an oxide ofgallium, an alkylammonium compound, and a base such as sodium hydroxide,ammonium hydroxide or ethylenediamine such that the initial reactantmolar ratios of water to silica range from about 5 to about 80,preferably from about 10 to about 50 and most preferably from about 20to about 40. In addition, preferable molar ratios for initial reactantsilica to oxide of gallium range from about 4 to about 200, morepreferably from about 10 to about 150 and most preferably from about 20to about 100. The molar ratio of base to silicon oxide should be aboutabove about 0.5, typically below about 5, preferably between about 0.05and about 1.0 and most preferably between about 0.1 and about 0.5. Themolar ratio of alkylammonium compound, such as tetra-n-propylammoniumbromide, to silicon oxide can range from 0 to about 1 or above,typically above about 0.005, preferably about 0.01 to about 0.2, mostpreferably about 0.02 to about 0.1.

The resulting slurry is transferred to a closed crystallization vesseland reacted usually at a pressure at least the vapor pressure of waterfor a time sufficient to permit crystallization which usually is about0.25 to about 25 days, typically is about one to about ten days andpreferably is about one to about seven days, at a temperature rangingfrom about 100° to about 250° C., preferably about 125° to about 200° C.The crystallizing material can be stirred or agitated as in a rockerbomb. Preferably, the crystallization temperature is maintained belowthe decomposition temperature of the organic template compound.Especially preferred conditions are crystallizing at about 165° C. forabout three to about seven days. Samples of material can be removedduring crystallization to check the degree of crystallization anddetermine the optimum crystallization time.

The crystalline material formed can be separated and recovered bywell-known means such as filtration with aqueous washing. This materialcan be mildly dried for anywhere from a few hours to a few days atvarying temperatures, typically about 50° to about 225° C., to form adry cake which can then be crushed to a powder or to small particles andextruded, pelletized, or made into forms suitable for its intended use.Typically, materials prepared after mild drying contain the organictemplate compound and water of hydration within the solid mass and asubsequent activation or calcination procedure is necessary, if it isdesired to remove this material from the final product. Typically, themildly dried product is calcined at temperatures ranging from about 260°to about 850° C. and preferably from about 425° to about 600° C. Extremecalcination temperatures or prolonged crystallization times may provedetrimental to the crystal structure or may totally destroy it.Generally, there is no need to raise the calcination temperature beyondabout 600° C. in order to remove organic material from the originallyformed crystalline material. Typically, the molecular sieve material isdried in a forced draft oven at 165° C. for about 16 hours and is thencalcined in air in a manner such that the temperature rise does notexceed 125° C. per hour until a temperature of about 540° C. is reached.Calcination at this temperature usually is continued for about 4 hours.The gallosilicate sieves thus made generally have a surface area greaterthan about 300 sq. meters per gram as measured by the BET procedure.

Although not required, it is preferred to employ the above-describedgallosilicate molecular sieve combined, dispersed or otherwiseintimately admixed in a matrix of at least one non-molecular sieve,porous refractory inorganic oxide matrix component, as the use of such amatrix component facilitates the provision of the ultimate catalyst in ashape or form well suited for process use. Useful matrix componentsinclude alumina, silica, silicaalumina, zirconia, titania, etc., andvarious combinations thereof. The matrix components also can containvarious adjuvants such as phosphorus oxides, boron oxides, and/orhalogens such as fluorine or chlorine. Usefully, the molecularsieve-matrix dispersion contains about 1 to 99 wt. % of a sievecomponent, preferably 40 to about 90 wt. % and most preferably 45 to 85wt. % of a sieve component based upon the sieve-matrix dispersionweight.

Methods for dispersing molecular sieve materials within a matrixcomponent are well-known to persons skilled in the art and applicablewith respect to the gallosilicate molecular sieve materials employedaccording to the preesnt invention. A method is to blend the molecularsieve component, preferably in finely-divided form, in a sol, hydrosolor hydrogel of an inorganic oxide, and then add a gelling medium such asammonium hydroxide to the blend, with stirring, to produce a gel. Theresulting gel can be dried, shaped if desired, and calcined. Dryingpreferably is conducted in air at a temperature of about 80° to about350° F. (about 27° to about 177° C.) for a period of several seconds toseveral hours. Calcination preferably is conducted by heating in air atabout 800° to about 1,200° F. (about 427° to about 649° C.) for a periodof time ranging from about 1/2 to about 16 hours.

Another suitable method for preparing a dispersion of the molecularsieve component in a porous refractory oxide matrix component is to dryblend particles of each, preferably in finely-divided form, and thenshape the dispersion if desired.

Alternatively, in another method, the sieve and a suitable matrixmaterial like alpha-alumina monohydrate such as Conoco Catapal SBAlumina can be slurried with a small amount of a dilute weak acid suchas acetic acid, dried at a suitable temperature under about 200° C.,preferably about 100° to about 150° C. and then calcined at betweenabout 350° and about 700° C., more preferably between about 400° toabout 650° C.

Silica-supported catalyst compositions can be made by dry mixing thegallosilicate sieve with a silica source such as Cab-O-Sil, adding waterand stirring. The resulting solid is then dried below about 200° C. andfinally calcined between about 350° C. and 700° C.

The platinum metal component of the catalyst employed according to thepresent invention can be present in elemental form, as oxides, asnitrates, as chlorides or other inorganic salts, or as combinationsthereof. While other Group VIII metals can be employed in the presentinvention, platinum is preferred because it is relatively inactive forhydrogenolysis which would result in undesirable increased yields of C₁and C₂.

Relative proportions of the sieve component and the platinum metalcomponent are such that at least a catalytically-effective amount ofeach is present.

The platinum metal component content preferably ranges from about 0.01to about 10 wt. %, calculated as a zero valent metal and being based onthe total weight of the catalytic final composite, with about 0.01 toabout 5 wt. % being more preferred, with a range of 0.05 to 1.0 wt. %being most preferred. Higher levels of platinum can be employed ifdesired, though the degree of improvement resulting therefrom typicallyis insufficient to justify the added cost of the metal.

The platinum metal component of the catalyst employed according to thisinvention can be associated with the sieve component by impregnation ofthe sieve component, or the sieve component can be dispersed in a porousrefractory inorganic oxide matrix, with one or more solutions ofcompounds of the platinum metal component which compounds areconvertible to oxides on calcination. It also is contemplated, however,to impregnate a porous refractory inorganic oxide matrix component withsuch solutions of the platinum metal component and then blend the sievecomponent with the resulting impregnation product. Accordingly, thepresent invention contemplates the use of catalysts in which theplatinum metal component is deposed on the sieve component, on a sievematrix component dispersion or on the matrix component of a sieve matrixcomponent.

The mechanics of impregnating the sieve component, matrix component ormatrix composite with solutions of compounds convertible to metal oxideson calcination are well-known to persons skilled in the art andgenerally involve forming solutions of appropriate compounds in suitablesolvents, preferably water, and then contacting the sieve matrixcomponent or sieve matrix dispersion with an amount or amounts ofsolution or solutions sufficient to deposit appropriate amounts of metalor metal salts onto the sieve or sieve matrix dispersion. Useful metalcompounds convertible to oxides are well-known to persons skilled in theart and include various ammonium salts as well as metal acetates,nitrates, anhydrides, etc.

In another embodiment of the present invention the platinum metalcomponent-gallosilicate containing catalyst also contains chloride. Theaddition of chloride to the catalyst serves to increase the conversionand selectivity of the process of the invention to aromatics. Aconvenient method of adding the chloride is to include a predeterminedvolume of a solution containing a predetermined concentration ofhydrochloric acid in the impregnating solution used to incorporate theplatinum metal component with the catalyst.

Alternatively, the chloride can also be added during the impregnation ofthe metal salt if the metal salt contains chloride, such as hydrogenhexachloroplatinate (H₂ PtCl₆.6H₂ O). If the chloride content in thechloride-containing metal salt is not sufficiently high, additionalchloride can be added by the addition of hydrochloric acid to theimpregnating solution.

In the instant embodiment of the invention the catalyst broadly contains0.1 to 10 wt. % chloride, preferably 0.5 to 5 wt. % chloride and mostpreferably 0.5 to 1.5 wt. % chloride based on the final catalyst weight.

Also contemplated within the purview of the present invention chloridecan be incorporated into the catalyst by the addition ofchloride-containing compounds to the feed stream such as carbontetrachloride, hydrochloric acid, in amounts such that the finalcatalyst contains the above prescribed amount of chloride.

The above-described catalysts can be employed in any suitable form suchas spheres, extrudates, pellets, or C-shaped or cloverleaf-shapedparticles.

The process of the present invention is carried out under suitableoperating conditions set out below in Table 3 under which the feed iscontacted with the above-described catalyst. It is also contemplatedthat a portion of the unconverted effluent stream can be recycled to thefeed after separation from the aromatic products.

                  TABLE 3                                                         ______________________________________                                                                      Most                                                        Broad    Preferred                                                                              Preferred                                       ______________________________________                                        Conditions                                                                    Temperature, °F.                                                                     700-1400   800-1200 850-1150                                    Total Pressure, psig                                                                         0-500      0-300    0-100                                      WHSV, h.sup.-1                                                                              0.1-100    0.1-40   0.1-20                                      ______________________________________                                    

The present invention is described in further detail in connection withthe following examples, it being understood that the same are forpurposes of illustration only and not limitation.

EXAMPLE 1

The present example demonstrates the process in accordance with thepresent invention.

A gallosilicate molecular sieve was prepared in a conventional mannerusing tetrapropylammonium bromide as the template compound and galliumoxide as the source of gallium. The gallium to silicon molar ratio ofthe finally prepared gallosilicate sieve was determined to be 0.069. Thesubject molecular sieve possessed an MFI or pentasil structure.

The so-prepared gallosilicate molecular sieve was subsequently dispersedin Catalpal B alumina (alpha alumina monohydrate) in amounts to achievea ratio of 45 wt. % sieve to 55 wt. % alumina. Specifically, thegallosilicate sieve powder and alumina powder were mechanically mixed,then blended with 5 % acetic acid to form a gel. This gel was dried at130° C. overnight and calcined in flowing air at 600° C. overnight.

The gallosilicate-alumina composition was then impregnated with anaqueous solution of tetraamine platinum (II) nitrate using the method ofincipient wetness impregnation. This impregnation resulted in acomposition having a 0.1 wt. % platinum content. This platinumimpregnated gallosilicate-alumina composition was then dried at 70° C.overnight followed by a calcination in flowing air at 1000° F. (538° C.)for 1 hour. The catalyst was then activated by drying it in flowingnitrogen at 1000° F. for a half-hour followed by a reduction step withhydrogen at 1000° F. for 1 hour.

The catalyst was then tested for propane conversion in a continuous flowfixed bed downflow reactor under the following conditions as set out inTable 4 below:

                  TABLE 4                                                         ______________________________________                                        Temperature       1000° F.                                             Pressure          50 psig                                                     Catalyst weight   1.5 g                                                       Propane liquid rate                                                                             24 ml/h                                                     Nitrogen diluent rate                                                                           100 cc (NTP) per minute                                     ______________________________________                                    

The above test resulted in a total conversion of 29.5 wt. %. Conversionis defined as the weight of all products in the effluent other than thefeed components, in this case propane, as a percentage of the weight ofthe feed components. The product distribution in wt. % is set out belowin Table 5.

                  TABLE 5                                                         ______________________________________                                        Methane            1.9                                                        Ethane             27.3                                                       C.sub.4 through C.sub.8 aliphatics                                                               16.9                                                       Benzene            13.0                                                       Toluene            22.2                                                       Ethylbenzene       1.0                                                        Para and metaxylenes                                                                             7.5                                                        Orthoxylene        1.5                                                        C.sub.9 + material 2.2                                                        Hydrogen           6.5                                                        ______________________________________                                    

The above product distribution shows the superior selectivity of theprocess of the invention. This is exemplified by the low C₁ and C₂ lightgas production, high hydrogen production, high concentrations ofbenzene, toluene and xylenes in the C₄ + product fraction and the lowC₉ + material production.

EXAMPLE 2

The present comparative example serves to show the superiority of theprocess of the invention over a prior art process that employs azinc-ZSM-5 catalyst.

Specifically, a ZSM-5 zeolite was prepared by digesting a mixture ofwater, sodium aluminate, Ludox AS-40 and tetra-propyl-ammonium bromidein an autoclave under autogeneous pressure at 300° F. Appropriateamounts of Ludox AS-40 and sodium aluminate were used to provide a SiO₂to Al₂ O₃ molar ratio of 30. The crystallized product was subsequentlyfiltered, washed repeatedly with distilled water and dried at 250° F.The so-dried material was then calcined at 1000° F. followed by anexchange with ammonium nitrate and a washing with distilled water.

The NH₄ -ZSM-5 zeolite was then exchanged with excess zinc nitrate threetimes followed by repeated washings with distilled water. Thezinc-exchanged ZSM-5 zeolite was then filtered and dried at 250° F. Thefinal catalyst had a zinc content of 1.02 wt. %. The Zn-ZSM-5 zeolitewas then wet-mulled and extruded with Catapal alumina to yield a1/16-inch extrudate containing 80 wt. % zeolite and 20 wt. % alumina.The extrusion step was followed by a drying step at 250° F. and acalcination step at 1000° F.

The platinum-gallosilicate catalyst used in the present example wasprepared substantially in the same manner as the platinum-gallosilicateprepared in Example 1. In this case, the catalyst contained gallium tosilicon ratio of 0.035.

The following Table 6 sets out results of a comparison pilot plant testof the Pt/Ga-silicate of the invention and the prior art Zn-ZSM-5 at thesame level of conversion.

                  TABLE 6                                                         ______________________________________                                        Comparison of Zn--ZSM-5 and Pt/Ga--Silicate                                   ______________________________________                                        Catalyst        Zn--ZSM-5   Pt/Ga--silicate                                                   (20% binder)                                                                              (45% binder)                                      Feed            100% C.sub.3 H.sub.8                                                                      100% C.sub.3 H.sub.8                              WHSV, g propane/g cat. h                                                                      9.4         9.4                                               Temperature, °F.                                                                       930         1000                                              Reactor pressure, psig                                                                        50          50                                                ______________________________________                                        Conversion per pass, % w/w                                                                           29     29                                              Hydrocarbon Distribution, % w/w                                               C.sub.1                19      3                                              C.sub.2                .sup. 22.sup.a                                                                       .sup. 24.sup.b                                  C.sub.4+  aliphatics   21     24                                              B                       7      9                                              T                      17     25                                              X                      10     12                                              C.sub.9+                4      3                                              C.sub.1,2  total       41     27                                              BTX total              34     46                                              ______________________________________                                         .sup.a C.sub.2 H.sub.4 /(C.sub.2 H.sub.4 + C.sub.2 H.sub.6) = 0.09 mole       fraction ethene                                                               .sup.b C.sub.2 H.sub.4 /(C.sub.2 H.sub.4 + C.sub.2 H.sub.6) = 0.01 mole       fraction ethene                                                          

The above Table clearly shows that the process of the inventionpossesses greater selectivity towards desirable BTX production, about35% greater, than the prior art process employing the Zn-ZSM-5 catalyst,and a lower selectivity towards C₁ and C₂ production, about 34% lowerthan the Zn-ZSM-5-process.

EXAMPLE 3

The present example is provided to show the stability of the catalystemployed in the process of the invention.

A catalyst prepared in substantially the same manner as the onedescribed in Example 1 was employed in the present example. Thiscatalyst contained a gallium to silicon molar ratio of 0.035.

Table 7 below shows the operating conditions employed and the resultsachieved when the process of the invention was carried out for anextended period of time using the above-described catalyst.

                                      TABLE 7                                     __________________________________________________________________________    Propane Aromatization on Pt/Ga--Silicate                                      __________________________________________________________________________    Catalyst            Pt/Ga--Silicate (60 wt. % Sieve)                          Temperature, °F.                                                                           1000°                                              Reactor pressure, psig                                                                            50                                                        Feed                100% C.sub.3 H.sub.8                                      WHSV, g propane/g cat. h                                                                          9.4                                                       __________________________________________________________________________    Time-on-stream, hour                                                                          1  2  3  4  5  6  7  8                                        Conversion per pass, wt. %                                                                    38.2                                                                             34.2                                                                             35.1                                                                             34.1                                                                             37.5                                                                             37.3                                                                             36.5                                                                             36.0                                     Hydrocarbon distribution, wt. %                                               Methane         3.0                                                                              2.3                                                                              2.4                                                                              2.3                                                                              2.8                                                                              2.4                                                                              2.5                                                                              2.4                                      Ethane          25.5                                                                             23.5                                                                             24.6                                                                             24.7                                                                             26.5                                                                             25.0                                                                             25.9                                                                             25.7                                     C.sub.4+  aliphatics                                                                          22.2                                                                             27.8                                                                             26.8                                                                             28.0                                                                             24.8                                                                             25.8                                                                             27.9                                                                             28.3                                     Benzene         9.8                                                                              8.0                                                                              7.9                                                                              7.5                                                                              9.3                                                                              8.5                                                                              7.8                                                                              7.7                                      Toluene         24.8                                                                             23.2                                                                             23.3                                                                             22.7                                                                             23.6                                                                             23.9                                                                             22.1                                                                             22.2                                     Xylenes (incl.  12.7                                                                             13.0                                                                             13.0                                                                             12.8                                                                             11.2                                                                             12.5                                                                             11.9                                                                             12.5                                     ethylbenzene)                                                                 C.sub.9+  aromatics                                                                           2.0                                                                              2.3                                                                              2.0                                                                              2.0                                                                              1.8                                                                              1.9                                                                              1.9                                                                              1.2                                      Selectivity to Aromatics                                                                      49.3                                                                             46.5                                                                             46.2                                                                             45.0                                                                             45.9                                                                             46.8                                                                             43.7                                                                             43.6                                     Yield of Aromatics                                                                            18.8                                                                             15.9                                                                             16.2                                                                             15.3                                                                             17.2                                                                             17.5                                                                             16.0                                                                             15.7                                     __________________________________________________________________________

The above table clearly shows that the catalyst of the invention possessstability or a relatively slow deactivation rate with respect toaromatics production. Also, the conversion per mass remained relativelyconstant.

EXAMPLE 4

The present example serves to show that the use of a gallosilicate sievein the absence of a platinum metal component not in accordance with thepresent invention results in a process possessing poor selectivity andconversion levels with respect to the desired aromatic products.

Specifically, a gallosilicate was prepared substantially as described inExample 1 except that the final gallium to silicon molar ratio was0.035. The gallosilicate was subsequently pressed into pill form, whichpills were subsequently comminuted and sieved to obtain 10-45 mesh sizeparticles.

The following Table 8 sets out the conditions and results used andobtained in the present example when this catalyst was used to producearomatics.

                  TABLE 8                                                         ______________________________________                                        Catalyst        Ga--silicate (100% molec. sieve)                              Temperature, °F.                                                                       930                                                           Reactor pressure, psig                                                                        50                                                            Feed            100% C.sub.3 H.sub.8                                          WHSV, g propane/g cat. h                                                                      9.4                                                           ______________________________________                                        Time-on-stream, h   1        2      3                                         Conversion per pass, wt. %                                                                        1.8      2.2    2.0                                       Hydrocarbon Distribution, wt. %                                               C.sub.1             17.7     18.4   18.2                                      C.sub.2             41.8     41.1   42.0                                      C.sub.4+  aliphatics                                                                              33.4     31.3   32.0                                      Benzene             1.2      1.5    1.3                                       Toluene             3.1      4.0    3.4                                       Xylenes (incl. ethylbenzene)                                                                      2.5      3.3    2.8                                       C.sub.9+  aromatics 0.3      0.4    0.3                                       ______________________________________                                    

The above table clearly shows poor conversion and poor selectivity toaromatics in the absence of a platinum metal component in the catalyst.

EXAMPLE 5

The present example when considered in conjunction with the results ofExample 3 serves to show that as the gallosilicate molecular sievecontent of the sieve-alumina matrix is increased while keeping theplatinum loading of the catalyst constant, the conversion increasesmarkedly while the selectivity to aromatics increases less significantlywhen the process of the invention is carried out.

The following Tables 9 and 10 set out the conditions employed andresults achieved for runs employing 13 wt. % sieve and 45 wt. % sieverespectively in the sieve-alumina matrix.

Each catalyst was prepared substantially as described in Example 1except for the sieve contents. Each catalyst contained 0.1 wt. % Ptbased on the final catalyst weight and each catalyst contained agallosilicate having a gallium to silicon molar ratio of 0.035.

                  TABLE 9                                                         ______________________________________                                        Catalyst          Pt/Ga--silicate (13% sieve)                                 Temperature, °F.                                                                         1000                                                        Reactor pressure, psig                                                                          50                                                          Feed              100% C.sub.3 H.sub.8                                        WHSV, g propane/g cat. h                                                                        9.4                                                         ______________________________________                                        Time-on-stream, h   1        2      3                                         Conversion, wt. %   11.5     11.0   10.5                                      Hydrocarbon Distribution, wt. %                                               C.sub.1             2.2      2.5    2.7                                       C.sub.2             19.9     20.3   20.6                                      C.sub.4+  aliphatics                                                                              39.3     39.6   39.9                                      Benzene             5.2      5.3    5.3                                       Toluene             18.3     18.2   17.7                                      Xylenes (incl. ethylbenzene)                                                                      11.5     11.0   10.7                                      C.sub.9+  aromatics 3.6      3.2    3.1                                       Selectivity to Aromatics, wt. %                                                                   38.6     37.7   36.8                                      Yield of Aromatics, wt. %                                                                         4.4      4.1    3.9                                       ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Catalyst          Pt/Ga--silicate (45% sieve)                                 Temperature, °F.                                                                         1000                                                        Reactor pressure, psig                                                                          50                                                          Feed              100% C.sub.3 H.sub.8                                        WHSV, g propane/g cat. h                                                                        9.4                                                         ______________________________________                                        Time-on-stream, h  1      2       3    4                                      Conversion, wt. %  28.0   30.2    30.7 30.0                                   Hydrocarbon Distribution, wt. %                                               C.sub.1            2.6    2.9     3.0  2.9                                    C.sub.2            23.5   25.4    26.2 26.1                                   C.sub.4+  aliphatics                                                                             24.4   22.5    22.2 23.8                                   Benzene            9.2    9.3     9.2  8.8                                    Toluene            25.3   25.6    25.5 25.1                                   Xylenes (incl. ethylbenzene)                                                                     12.4   12.0    11.7 11.5                                   C.sub.9+  aromatics                                                                              2.6    2.3     2.2  2.0                                    Selectivity to Aromatics, wt. %                                                                  49.5   49.2    48.6 47.4                                   Yield of Aromatics, wt. %                                                                        13.9   14.9    14.9 14.2                                   ______________________________________                                    

When the results of the above Tables 9 and 10 are compared with Table 7it is clear that increasing the sieve content increases conversion andaromatics selectivity.

EXAMPLE 6

The present example serves to show that the addition of chloride to thecatalyst in accordance with the invention results in enhanced conversionand selectivity to aromatics.

In the present example a gallosilicate MFI zeolite having a gallium tosilicon molar ratio of 0.035 was drymixed with Catalpal alumina(alpha-alumina monohydrate) to obtain 60 wt. % sieve-40 wt. % aluminamatrix. Five percent acetic acid was then added to the powder till apaste was formed. During the addition of acetic acid, the wetted powderwas continually stirred. The paste was dried overnight in a vacuum ovenat 70° C. followed by calcination in a muffle furnace under air flow at1100° F. for 18 hours. The gallosilicate-alumina matrix was thencomminuted and sieved to obtain 10 to 45 mesh size particles. Theplatinum and chloride were added to the gallosilicate-alumina byincipient wetness impregnation. A predetermined amount of tetraamineplatinum (II) nitrate and a predetermined amount of a 1M hydrochloricacid solution and distilled water were added together to yield theimpregnating solution. After impregnation, the catalyst particles weredried at 70° C. in a vacuum oven overnight followed by calcination in amuffle furnace under air flow at 1000° F. for two hours. Enoughtetraamine platinum (II) nitrate and hydrochloric acid were added togive 0.1 wt. % Pt and 1.0 wt. % Cl.

The following Table 11 sets out the conditions employed and the resultsachieved in the present example carried out in accordance with thepresent invention.

                  TABLE 11                                                        ______________________________________                                        Catalyst        Pt/Ga--silicate/Cl (0.1 wt. % Pt,                                             1.0 wt. % Cl, 60% sieve)                                      Temperature, °F.                                                                       1000                                                          Reactor pressure, psig                                                                        50                                                            Feed            100% C.sub.3 H.sub.8                                          WHSV, g propane/g cat. h                                                                      9.4                                                           ______________________________________                                        Time-on-stream, h  1      2       3    4                                      Conversion, wt. %  46.3   45.8    46.8 46.6                                   Hydrocarbon Distribution, wt. %                                               C.sub.1            5.0    5.2     5.2  5.5                                    C.sub.2            34.8   36.0    35.6 37.2                                   C.sub.4+  aliphatics                                                                             11.4   11.6    11.3 11.1                                   Benzene            12.5   13.2    13.5 13.4                                   Toluene            23.1   22.1    22.5 21.6                                   Xylenes (incl. ethylbenzene)                                                                     10.1   9.2     9.2  8.7                                    C.sub.9+  aromatics                                                                              3.1    2.7     2.7  2.5                                    Selectivity to Aromatics, wt. %                                                                  48.8   47.2    47.9 46.2                                   Yield of Aromatics, wt. %                                                                        22.6   21.6    22.4 21.5                                   ______________________________________                                    

The above table shows when compared with Table 7 (no chloride addition)that the addition of chloride increases the conversion and selectivityto aromatics. The C₁ and C₂ yields, however, are greater than in thecase where chloride is not present.

What is claimed is:
 1. A process for converting a gaseous hydrocarbonfeed containing paraffinic hydrocarbons to aromatic hydrocarbons whichcomprises contacting the feed under conversion conditions with acatalyst composition comprising a gallosilicate molecular sieve, aplatinum metal component and a chloride component present in an amountranging from about 0.1 to about 10 wt. % based on the total weight ofthe composition.
 2. The process of claim 1 wherein the gaseous feedcomprises C₂ through C₅ paraffins.
 3. The process of claim 1 wherein thegaseous feed comprises propane.
 4. The process of claim 1 wherein thegallosilicate molecular sieve is dispersed within a non-molecular sievecontaining porous refractory inorganic oxide matrix component.
 5. Theprocess of claim 1 wherein the platinum metal component is present in anamount ranging from about 0.01 to about 10 wt. % calculated as the zerovalent metal and based on the total weight of the composition.
 6. Theprocess of claim 4 wherein the gallosilicate molecular sieve is presentin the dispersion such that the weight of the gallosilicate ranges fromabout 45 to 85 wt. % based on the weight of the gallosilicate -refractory inorganic oxide dispersion.
 7. The process of claim 4 whereinthe refractory inorganic oxide component is selected from a groupconsisting of silica, silica-alumina, and alumina.
 8. The process ofclaim 1 wherein the platinum metal component is present in an amountranging from about 0.01 to about 5 wt. % calculated as the zero valentmetal and based on the total weight of the composition.
 9. The processof claim 1 wherein the platinum metal component is present in an amountranging from about 0.05 to about 1.0 wt. % calculated as the zero valentmetal and based on the total weight of the final composition.
 10. Aprocess for converting gaseous hydrocarbons in a feed comprisingparaffinic hydrocarbons and a chloride-containing compound to aromatichydrocarbons which comprises contacting the feed under conversionconditions with a catalyst composition comprising a gallosilicatemolecular sieve and a platinum metal component.
 11. The process of claim10 wherein the chloride-containing compound is carbon tetrachloride andis present in an amount such that the catalyst composition acquiresabout 0.1 to about 10 wt. % chloride based on the total weight of thecomposition from the carbon tetrachloride in the feed.